High speed infrared film



WJBARTH ET' 2,134,546 HIGH SPEED INFRARED FILM Filed July 14, 1936Infra-red sensitive layer panchromatic ayer upport WdZt/ze r 190ml):vHermann h. Duerr INVENTORS BYWQQEISQ;

THEIR ATTORN Patented Oct. 25, 1938 UNITED STATES PATENT OFFICE.

HIGH SPEED INFRARED FIL'M Application July 14, 1936, Serial No. 90,568

6 Claims.

The present invention relates to high speed infra-red sensitizedphotographic films which are particularly suitable for use in aerialphotography and the like. I

It is well known that pictures taken with infrared sensitizedphotographic emulsions bring out details of the subject photographedrather vividly.

- As a matter of actual fact, in some cases it is the taking of pictureswhich are to appear as if they had been taken at night .when actuallyeiiiposure is made in bright daylight under clear s es.

The use of infra-red sensitive emulsions in these fields, however, hasbeen to a large extent hampered by the fact that such emulsions have thedisadvantageous property of being of a relatively low speed as theirsensitivity is much less than that of ordinary emulsions of the.panchromatic type. The difierence in speed between these two types ofemulsions is especially noticeable when red or yellow filters are used.Thus the art up to the present time has not been able to find aninfra-red sensitizing dyestuff which is capable of imparting anintensity comparable to that obtainable with dyestuffs generallyutilized for sensitizing emulsions for the orange and red part of thespectrum.

The purpose of the present invention is to v overcome this speeddeficiency of infra-red sensitized emulsions so as to take fulladvantage of the property of said emulsions to vividly reproduce detailsand thus render said emulsions excellently suitable for use in aerialphotography and the like.

In general we effect this object by supplementing the sensitivity of theinfra-red emulsion by an additional emulsion which is panchromaticallysensitized. It would appear ofihand that having once recognized that apanchromatic sensitized emulsion is capable of augmenting thesensitivity of an infra-red sensitized emulsion, it would be unnecessaryto take any precaution with regard to the method of incorporating thesensitizing elements in the film. Thus it would appear pos-' sible toeffect the desired result by sensitizing a single emulsion for both thered and infra-red portions of the spectrum. We have ascertained,

however, that when using an emulsion sensitized by a mixture ofpanchromatic and infra-red sensitizing dyes, the sensitivity of thepanchromatic sensitization is so much greater than the infra-redsensitization that the resulting image 5 is predominantly that of thepanchromatic emulsion and little or no effect is visible from theinfra-red sensitization. In other words, the picture taken with suchemulsions displays the characteristics of a panchromatic emulsion ratherthan those of an infra-red emulsion.

It would also seem that the'desired result could be obtained byproviding two separate emulsions sensitized panchromatically forinfra-red and arranging the panchromatic sensitized emulsion over theinfra-red sensitized emulsion. However, if the infra-red sensitizedemulsion is the undercoating and the panchromatic sensitized emulsionthe overcoating, the panchromatic sensitivity' will predominate andcause the resulting picture to display the characteristics of a panchromatic emulsion, thus nullifying the property of the infra redsensitized emulsion to bring out distinctly the details of the subjectphotographed. It has been discovered by us that the only way that thesensitivity'of the infra-red emulsion can be augmented by a panchromaticsensitized emulsion while preserving the characteristics of theinfra-red emulsion is by locating the infra-red sensitized emulsion overthe panchromatic sensitized emulsion. It ispossible by this method todepress the sensitivity of the panchromatic emulsion to such an extentthat the resulting picture will partake predominantly of thecharacteristics of those produced from infra-red sensitized emulsions.The degree of sensitivity furnished by the panchromatic undercoating canbe controlled by the sensitivity of this emulsion itself. Preferably,however, this is done by adjusting the thickness of the infra-redsensitive top layer. The greater the thickness of the top layer, themore depressed will be the sensitivity of the underlying panchromaticlayer. The contrast of the panchromatic layer is diminished at the sametime by the top coating. For best results we use an infra-red sensitizedemulsion having a thickness varying from 6 to 16/ At such thicknessesthe panchromatic emulsion will furnish just enough additionalsensitivity to give the film a speed, when used with red filters, whichis from 10.0 to 200% greater than that of the infra-red emulsion alone..I

The fllm is made up according to the usual method of coating;gelatino-silver-halide emulsions containing sensitizing dyes on a filmbase 5 such as nitroor acetyl cellulose. For sensitizing the infra-redemulsion, we may employ dyestufis usual for this purpose such asbis-[l-ethylquinoline(4) l-trimethinecyanine iodide having the followingstructure and sold under the trade name Rubrocyanin,bis-[1-ethy1-quinoline(4)] p (1'-ethyl-1-iodoquinoline-4'-methylene)-trimethinecyanine iodide having the following structure and sold underthe trade name Allocyanin or other infrared sensitizing dyes. Similarlythe dyestuffs ordinarily employed for sensitizing emulsions in the redportion of the spectrum such as bisl-ethyl-quinoline (2)l-trimethinecyanine iodide having the following structure on=cncn N mCzHa CsHt and sold under the trade name Pinacyanol or other sensitizingdyes for the red portion of the spectrum may be utilized for thepanchromatic emulsion.

In forming the image, the panchromatic layer, because of its greatersensitivity, registers the darker parts of the subject, as well as thebrighter parts. However, due to the very fiat gradation caused by thetop layer, acting in a sense as a light restraining layer, the imageregistered is relatively fiat. The top layer, because of its'very steepgradation, superimposes an image on the first layer, especially in thebrighter parts of the subject, which is of high contrast but which doesnot destroy the darker parts of the image formed in the panchromaticlayer. The result is a satisfactory image having the contrastycharacteristics of the infra-red and at the same time still showingregistration of the dark portions of the subject due to the greatersensitivity of the pan chromatic layer,

In practice it has been found advantageous to make the panchromaticlayer inherently fiat in gradation in its red sensitized region byrestricting the amount of panchromatic sensitizer. For example, themaximum sensitivity and maximum gradation 01 an emulsion sensitized withPinacyanol may be obtained by using 15 to 20 mg. Pinacyanol per oneliter of emulsion. By using, for instance, only 4 to 8 mg. of thissensitizing dye per one liter of emulsion, thegradation of the resultingemulsion in the red region is decidedly The top infra-red layer furtherdepresses the gradation of the panchromatic layer so that there isdeliberately provided in the film a panchromatic layer of very flatgradation, that is, substantially below maximum gradation, whichregisters the total image in very fiat gradation. Upon this image isthen superimposed the contrasty image characteristic'of the infra-redlayer, the final image retaining the fiat registration of the darkerparts of the subject provided by the sensitive panchromatic layer.

Our invention will be further explained by reference to the followingspecific examples when taken with the accompanying self-explanatorydrawing of a section through a film according to the present invention.It is to be understood, however, that our invention is not restricted tothese specific examples but that the examples are submitted forillustrative purposes only.

Example 1 A film is constructed with a base of acetyl cellulose, agelatino-silver halide emulsion panchromatically sensitized withPinacyanol on said base and a gelatino-silver halide emulsion sensitizedto infra-red by means of Rubrocyanin on said panchromatic emulsion. Theinfra-red sensitized layer is cast to a thickness of 10-12//l.. Thequantity of dyestufi to gelatine in the panchromatic emulsion is about60 mg. of dyestufl' per kilogram of gelatine whereas in the outeremulsion the quantity of dyestufi to gelatine is about 10 mg. per kg. ofgelatine.

Example 2 The film is constructed in the same way except that the outeremulsion is sensitized to infra-red by means of Allocyanin.

Films of this construction after exposure may be developed and printedin the usual manner. Due to the presence of the panchromaticallysensitized layer, the films have a speed which fits them for use infields such as aerial photography which require films of speeds as highas of a second. Despite this high speed, the films nevertheless arepossessed of the valuable haze-cutting characteristics so peculiar toinfra-red sensitized films.

What -we claim is:

v 1. A high speed infra-red film comprising a base, .a colorlesspanchromatic sensitized emulsion on said base and a colorless infra-redsensitized emulsion on said panchromatic sensitized emul- 81011.

2. A high speed infra-red film comprising a base, a colorlesspanchromatic sensitized emulsion on said base and a colorless infra-redsensitized emulsion on said panchromatic sensitized emulsion, saidinfra-red emulsion having a thickness of from 6 to 16/p.

3. A high speed infra-red film comprising a base, a colorlessgelatino-silver halide emulsion infra-red emulsion withbis-[l-ethyl-quinoline(4) l-trimethinecyanine iodide.

5. A high speed infra-red fllm comprising-a base; a colorlesspanchromatic sensitized emulsion on said. base which is inherently flatin gradation in its red sensitized region and a colorless infra-redsensitized emulsion on said panchromatic sensitized emulsion.

6. A film as defined in claim 5 wherein the panchromatic emulsioncontains from 4 to 8 mg.

of sensitizing dye per liter of gelatine.

' WAL'I'HER BAR'I'H.

HERMANN H. DUERR.

